It is known that a solenoid valve is used as a controllable damping valve capable of controlling a damping force of a shock absorber interposed between a chassis and an axle of a vehicle. In JP 2009-222136 A, there is discussed such a solenoid valve. The solenoid valve includes an annular valve seat provided in a main flow passage connected from a cylinder of the shock absorber to a reservoir, a main valve body seated on or unseated from the annular valve seat to open or close the main flow passage, a pilot passage branching from the main flow passage, an orifice provided in the pilot passage, a back-pressure chamber provided in a rear face side of the main valve body opposite to the valve seat side, a pilot valve provided in a downstream of the pilot passage, and a solenoid configured to control a valve opening pressure of the pilot valve.
A secondary pressure downstream from the orifice in the pilot passage is introduced into the back-pressure chamber, and the main valve body is pressed by the secondary pressure. Since the pilot valve is provided downstream from the back-pressure chamber, the secondary pressure introduced into the back-pressure chamber is controlled by the valve opening pressure of the pilot valve by adjusting the valve opening pressure of the pilot valve using a thrust force of the solenoid.
The secondary pressure is applied to the rear face of the main valve body to exert a force such that the main valve body is pressed toward the valve seat side. A pressure is applied from the upstream of the main flow passage to the front face of the main valve body to exert a force such that the main valve body is flexed and is unseated from the valve seat. Therefore, the main valve body is opened when the force of unseating the main valve body from the valve seat by virtue of the pressure from the upstream side of the main flow passage exceeds the force of pressing the main valve body to the valve seat by virtue of the secondary pressure.
That is, it is possible to adjust the valve opening pressure of the main valve body by controlling the secondary pressure. Therefore, the solenoid valve can change resistance to the liquid flow passing through the main flow passage by adjusting the valve opening pressure of the pilot valve using the solenoid so that a desired damping force can be generated in the shock absorber.